The De-Ice Man Cometh

Snow, Ice, and Airplanes. Everything You Need to Know About the Travails of Winter Flying.

2024 Version.

Deiceman

IT’S THAT TIME OF YEAR AGAIN: snowstorms, cancellations, the sights and sounds of that weird fluid splattering off the fuselage…

 

On the Ground:

Parked at the terminal, ice, snow, or frost accumulates on a plane the same way it does on your car. But while a cursory brushing or scraping is a safe-enough remedy for driving, it doesn’t work for flying, when even a quarter-inch layer of frozen material can alter airflow around the wing—highly important during takeoff, when speed is slow and lift margins are thin. The delicious-looking spray used to clean it away is a heated combination of propylene glycol alcohol and water. Different mixtures, varying in temperature, viscosity, and color, are applied for different conditions, often in combination: a plane will be hit with so-called Type I fluid (orange) to get rid of the bulk of accumulation, then further treated with Type IV (greenish), a stickier substance that wards off additional buildup.

While it might appear casual to the passenger, the spraying procedure is a regimented, step-by-step process. Pilots first follow a checklist to ensure their plane is correctly configured. Usually the flaps and slats will be lowered to the takeoff position, with the APU providing power and the main engines shut down. The air-conditioning units will be switched off to keep the cabin free of fumes. When deicing is complete, the ground crew tells the pilots which types of fluid were used, as well as the exact time that treatment began. This allows us to keep track of something called a “holdover time.” If the holdover time is exceeded before the plane has a chance to take off, a second round of spraying may be required. The length of the holdover depends on the kind of fluids used, plus the rate and type of active precipitation (dry snow, wet snow, ice pellets; light, moderate, heavy). We have charts to figure it all out.

Deicing fluid isn’t especially corrosive, but neither is it the most environmentally friendly stuff in the world. And although it resembles apple cider or a tropical fruit puree, I wouldn’t drink it; certain types of glycol are poisonous. At upward of $5 a gallon, it is also very expensive. When you add in handling and storage costs, relieving a single jet of winter white can cost several thousand dollars. A growing number of airports recycle deicing fluid. It’s a complicated process, but it beats letting the goop seep into the water table or drain into lakes and rivers.

Another method is to tow aircraft into specially built hangars equipped with powerful, ceiling-mounted heat lamps. JetBlue has such a hangar at JFK. In some ways this is a greener technique, though it uses hideous amounts of electricity.

 

In the Air:

Under the right combination moisture and temperature, icing also can occur during flight. It tends to build on the forward edges of the wings and tail, around engine inlets, and on various antennas and probes. Left unchecked, it can damage engines, throw propeller assemblies off balance, and disrupt the flow of air over and around the wing. In a worst-case scenario, it can induce a full-on aerodynamic stall.

The good news is that all commercial aircraft are equipped with devices to keep these areas clean. On propeller-driven planes, pneumatically inflated “boots” will break ice from the leading edges of the wings and horizontal tail. On jets, hot air from the engine compressors is ducted to the wings, tail, and engine intakes. Windshields, propeller blades, and the different probes and sensors are kept warm electrically. These systems use redundant power sources and are separated into independently functioning zones to keep any one failure from affecting the entire plane.

Airframe ice comes in three basic types: rime, clear, and mixed. Rime is the most frequent one, appearing as a sort of white fuzz. The rate at which ice accretes is graded from “trace” to “severe.” Severe icing, usually associated with freezing rain, can be a killer. It’s also very rare, and it tends to exist in thin bands that are easy to avoid or fly out of. On the whole, inflight icing is considerably more of a threat to smaller, noncommercial planes than it is to airliners. Even in the heaviest precipitation, seeing more than a trace amount of rime on a jet is uncommon.

Planes also have sophisticated anti-skid systems to help deal with slick runways. And if you’ve looked closely, you’ve seen that most runways are cut laterally by thousands of thin grooves, spaced inches apart, to help with traction. When it’s icy or snowy we get braking reports, graded 1-5, or from “good” to “nil,” prior to taking off or landing. Anything below a 2, or if described as worse than “poor,” and the runway essentially becomes unusable. Slippery conditions reduce the amount of crosswind we’re allowed to take of or land with, and a runway will be further off-limits if the depth of snow or slush exceeds a certain value. It varies by aircraft type and carrier-specific rules, but more than about three inches of dry snow on a runway, or a half-inch of the wet stuff, and you aren’t going anywhere until it’s plowed.

I’ve made my share of wintry-weather landings. One thing that always surprises me is the way in which fresh snowfall can make a runway difficult to see and align yourself with. In normal conditions the runway sits in stark contrast to the pavement, grass, or whatever else is around it. When it’s snowing, everything is white. Runways are outfitted with an array of color-coded lighting. Most of the time you pay only cursory attention to these displays. That is, until the moment you break from a low overcast, just a few hundred feet over the ground with a half-mile of visibility, and find yourself confronted with a landscape of undifferentiated whiteness. Those lights and colors are suddenly very helpful.

 

Accidents and Incidents:

There have been tragedies over the years in which planes attempted takeoff with iced-over wings. Most recent was a 1992 USAir incident at LaGuardia. Nine years earlier was the infamous Air Florida disaster in Washington, DC, when in addition to ignoring buildup on the wings, the crew failed to run the engine anti-ice system, allowing frozen probes to give faulty thrust readings. On Halloween night in 1994, sixty-eight people died aboard American Eagle flight 4184 — a crash attributed to a design flaw, since rectified, in the ATR-72’s deicing system. Other planes have gone skidding off the end of snowy runways. Culprits have included erroneous weather or braking data, an unstable approach continued when it should have been broken off, the occasional malfunction, or any combination of those things.

I can’t tell you there will never be another ice-related accident. But I can assure you that airlines and their crews take the issue a lot more seriously than they used to. We’ve learned a lot — much of it the hard way — and this has carried over into a mindset, and more careful procedures, that leave little to chance.

If it seems like the effects of winter storms become worse, that’s because they have. When I was a kid growing up near Boston, a few inches of snow at Logan Airport meant almost nothing. Nowadays, the slightest dusting and the airport goes bonkers with cancellations and delays. What’s happened, for one, is that the amount of air traffic has more than doubled since then. In the 1980s, closing a runway for 35 minutes for plowing had comparatively mild repercussions. Today, hundreds of flights are impacted.

Airlines also have become more conservative when bad weather looms, preemptively readjusting their schedules before the brunt of any storm moves in. This is unfortunate if you’re one of those whose flight is canceled in advance, but things would be a lot worse, for a lot of people, had the airline attempted to push through. And what’s happening in one part of the country affects flights, and their passengers, further down the chain, in cities across the nation and the world. Drawing down the operation in one location protects passengers elsewhere.

When it gets bad, airline workers don’t enjoy the chaos any more than passengers do. Pilots and flight attendants often live in cities far from their crew bases, and have to fly in to catch their assignments. With a storm looming, that means leaving many hours early — sometimes a day or more ahead of schedule. Or, on the back end, we can find ourselves unable to get home again until things return to normal.

Once in a while, though, the timing works to our advantage. How do you turn what was supposed to be a 24-hour European layover in into a six-day vacation, as happened to me a couple of winters ago? Easy, just send a snow hurricane roaring through the Northeast. While the rest of you were stranded on tarmacs, sleeping under benches and sucking on discarded Chick-fil-A wrappers, I was sightseeing and sipping hot chocolate.

Not to rub it in or anything.

 

Iceman photo by the author.

“When you’re sitting on the tarmac while a guy in a hovering pod floats over you, twin beams of light piercing the murk of de-icing fluid. That’s my airplane fantasy. I want to be that guy!”

— Peter Hughes, Ask the Pilot fan and bassist for the Mountain Goats.

 

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December 10, 2015 · Filed under Uncategorized